1. Field of the Invention
The present invention relates to a numerical control apparatus for controlling a machine tool, and more particularly, to a numerical control apparatus for controlling a machine tool which machines prototypes or the like.
2. Description of the Related Art
Advances in the technology of numerically controlled machine tools have been so great that they can machine workpieces of complex shape at high speed with precision. At present, workpieces of complex shape cannot be machined without numerically controlled machine tools.
To generate machining programs, there are widely used interactive numerical control apparatus which comprise a numerical control apparatus with an interactive program generating function, and automatic programming apparatus for simply generating complex machining programs.
In the use of such numerical control apparatus, it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data for generating strict machining programs. The interactive numerical control apparatus and the automatic programming apparatus can be used to machine a number of workpieces.
For some machining processes for producing a prototype or a model, general-purpose milling machines, lathes, and the like are used which require less time to carry out preparatory action such as attachment and detachment of workpieces, installation of tools, etc., and does not require less time to generate machining programs. Machining on such machines or lathes has been carried out solely at the determination of the operator.
Problems of general-purpose machine tools are that available operators who can handle general-purpose machine tools decrease, and that it is difficult for the general-purpose machine tools to carry out oblique linear machining, arcuate machining, or the like though they can effect linear machining without any problem.
If, on the other hand, a general numerically controlled machine tool is used to machine a prototypes or a model, then it is necessary to accurately define machine coordinates, a machine origin, program coordinates, a machining origin, and other data. While it is not impossible to define those data, the required programming process is too time-consuming and troublesome for machining a portion of a single workpiece.
To solve the above problems, the applicant has filed Japanese patent application No. 4-231836 on a numerical control apparatus which employs a general-purpose machine tool for carrying out simple machining processes to machine prototypes or the like.
Such a numerical control apparatus feeds a tool during machining in accordance with an operator's operation of a manual pulse generator and jog feed buttons. An operator machines a workpiece while checking machining processes and stops the operation at the time when the machining is completed. Therefore, if there is a delay in the operator's stop operation, the tool continues to be moved and unnecessary machining actions are carried out. If the tool is exceedingly fed due to a careless operation, the tool may strike any object other than the workpiece, which is dangerous.
For carrying out simple machining processes to machine prototypes or the like, generally, the operator operates the manual pulse generator and the jog feed buttons to machine a workplace while checking the machining processes in order.
Accordingly, while it is possible to switch a single pulse generator to use for controlling respective axes, operability of the numerical control apparatus is impaired since frequency of switching action increases.
Conversely, if a handle for moving the tool corresponding to a designated shape such as an oblique straight line, circular arc, or the like is separately provided as well as handles for respective machining axes in X-axis, Y-axis, and Z-axis direction, additional cost is required.
Furthermore, with the numerical control apparatus mentioned above, designation of a tool moving direction is easy if the tool is to be moved in the direction parallel to either the X-axis, Y-axis, or Z-axis. However, when it is required to move the tool in two or more axis directions simultaneously as is the case to machine an oblique straight line, circular arc, or the like, much time and labor are required since the tool is not necessarily moved in the desired direction by a simple operation of the manual pulse generator and jog feed buttons.